A knock-out engine performance

An improved formula for a gasoline
additive has been developed by researchers from KAUST and oil company
Saudi Aramco. The new mixture of butanol additives reduces engine
knocking, a major obstacle to improved engine performance.

In
spark ignition engines, a gasoline–air mixture is ignited with a spark
plug, and the energy of the burning fuel is used to drive the motor.
Engine knock, which is caused by fuel igniting at the wrong moment,
leads to an uneven running of the motor and a reduced performance in
advanced engine types.

“Engine knock is a limiting factor
particularly when it comes to increasing the efficiency of engines
through downsizing or turbocharging,” said Aamir Farooq from KAUST’s
Clean Combustion Research Center.

Knocking can be reduced by
introducing additives to the gasoline, which suppress disruptive
ignition events. However, many existing additives are hazardous. They
typically dissolve in water, which can harm the environmental and, if
there is a gasoline leak, may threaten human health.

Ethanol is an
environmentally-friendly replacement additive obtained from biological
materials, and it is widely used as a biofuel. Ethanol does, however,
mix with water, hampering the possibility to transport gasoline through
pipelines over longer distances.

Butanol compounds are good
alternatives as they have a similar chemical structure to ethanol, but
they have more carbon atoms per molecule and boast a higher energy
density per molecule. Another advantage is that they mix less with
water, making the transport through oil pipelines more feasible.

Instead
of looking at the individual performance of known butanol additives,
the researchers studied mixtures of butanol compounds. This allows for
the optimization of their anti-knock properties. The experiments were
supported by complementary simulations using a theoretical chemical
kinetic model that describes the fuel ignition process and the
performance at different temperatures and pressures.

The combined
practical and theoretical results demonstrate that the butanol mixture
improves the performance of gasoline engines at typical operating
temperatures, assisted by the interaction of the additives with the
primary fuel in the engine.

The findings show the practical
viability, says Farooq, because “the mixed butanols we studied are
products of well-established refining processes and hence their supply
is reliable and continuous.”

Improved and more environmentally
friendly gasoline mixtures might soon be a reality and would enable the
development of higher-performing engines.